1. Field of the Invention
The present invention relates to medical apparatus and methods and more particularly to electroconvulsive therapy (ECT) apparatus and method for preventing an excessive or insufficient stimulus dosage.
2. Description of the Related Art
In electroconvulsive therapy (ECT), using "bitemporal" electrode positioning, generally two electrodes are applied to the temple of the patient during the treatment session. One electrode is positioned on the temple's left side and the other on the temple's right side. A small electric current, called the "stimulus dosage", is applied for less than ten seconds between the two electrodes. Alternatively, the electrodes may be positioned anterior bilaterally or unilateral. Only a small portion of the current reaches the brain because most is deflected by the skull.
It has recently been shown that when administered according to accepted standard of practice (American Psychiatric Association, APA, 1990). electroconvulsive therapy (ECT) is a safe procedure that does not have a measurable risk of brain injury. The APA standard of practice includes a limitation of the stimulus dosage administered to the patient, because of the expectation that unnecessarily high stimulus dosages may cause adverse effects to the patient. To accomplish the delivery of a stimulus dosage within operator specifications, i.e., the stimulus dosage determined by the attending physician, existing ECT devices rely on a calibration, or test, conducted prior to initiation of the stimulus or during periodic maintenance checks on the ECT device. Once the stimulus dosage has been initiated, delivery of an accurate dose, for example, within the APA standard, has relied solely on the circuits of the ECT device that generate the stimulus. There has been no separate circuit or device to monitor and measure the stimulus dosage during its application, and to terminate the stimulus in the event it exceeds the operator's specification, i.e., the operator's setting of the dosage on a dial of the ECT device.
In the event of failure of an electronic component it is possible for existing ECT devices to deliver an electrical stimulus dose that substantially exceeds the operator's specification. It is also possible that such a dosage would exceed the maximum indicated by a national or international agency that publishes, or could publish, standards for ECT devices, e.g., the IEC--International Electrotechnical Commission 601-2-14; the APA--American Psychiatric Association; the FDA--Food and Drug Administration. Such an excessive dosage may inadvertently, and unnecessarily, expose the patient to a dose that exceeds the published limitations for ECT devices.
A "worst-case" scenario would be the exposure of the patient to line current, as might occur in failure of the ECT device's transformer, for example, a transformer short circuit due to insulation breakdown. Although the likelihood of such an occurrence is extremely remote, such a possibility must nevertheless be considered because of the life and death nature of such exposure.
Existing test methods employed to evaluate the safety of the stimulus prior to ECT are limited to measuring the skin impedance of the patient by applying impalpable electrical trickle currents to the patient's skin. However, such skin impedance test circuits cannot prevent the patient from receiving an excessive electrical dosage that may be delivered in the event of component failure in the ECT device, because such skin impedance test circuits do not monitor the actual stimulus.
In ECT, the physician determines the stimulus dosage, i.e., the length and strength of the applied current. He takes into account such factors as the patient's age, size, physical condition and prior history of ECT treatments. The seizure threshold systematically increases with age. The physician may, with presently available apparatus, reasonably and accurately select the desired electrical duration. For example, in the "Thymatron-DGx" ECT instrument (TM of Somatics, Inc., Lake Bluff, Ill.) the stimulus may be selected to be a brief series of electrical square waves, providing a constant current of 0.9 amps limited to 500 volts, consisting of 60-140 bipolar pulses per second of 1 msec width, which is adjustable, by the physician, 0.1-8.0 second in duration. Alternatively the dosage may be administered in groups of pulses, pacing them over a period of up to 8 seconds.
Generally the physician will determine the stimulus dosage and set that selection in the ECT device by setting a stimulus dial. The ECT device, in the case of the "Thymatron-DGx" device, has factory preset pulsewidth, frequency and duration which corresponds to each stimulus dial setting. Alternatively, the physician may elect to set other pulsewidths, frequencies and durations within the range 30-70 Hz and 0.5 to 1.5 msec.
In U.S. Pat. No. 5,269,302 to Swartz and Abrams, an ECT device includes a special-purpose electromyograph (EMG) to detect muscle activity. In U.S. Pat. No. 4,873,981 to Abrams and Swartz the ECT device includes a system to automatically monitor and display the occurrence and duration of an induced EEG seizure. In U.S. Pat. No. 4,709,700 to Hyrman an ECT device uses short pulses of 20-100 microseconds and unidirectional electric direction. The Hyrman patent, incorporated by reference herein, discusses the techniques of "ergometry" (measurement of ECT dose in pulses) and "coulometry" (total charge which flows during treatment).